Why is my free memory constantly decreasing? A year ago, I had 50GB. Then after 4 months without checking my free memory, I had 9GB. After that:
8.5, 7.6, 5.2, 3.3, 2.1, 1.89, 1.77, 1.56, 1.21, 912MB; Then I deleted some movie
1.9GB, 1.81, 1.5, and now 1.33GB.
And I suppose It will continue that. How to stop this?

You also need to do a full virus and malware scan. If you aren't already using it, download Microsoft Security Essentials, and install it and run a full scan. Also, get a copy of Malware Bytes and SUPERAntiSpyware and run the full scans from each of those. If you don't have enough free space to install Malware Bytes and SUPER, you can use them from a USB drive, just leave it plugged in and install to the drive letter for the drive.

@og
I have scanned the disk with Advanced SystemCare, and I have fixed many problems. But still nothing.

Never mind that. SpaceSniffer proved wrong:My thinking as a computer rookie is that a program called RstIdle is doing this. He always comes back even doe I always kill him. It takes more than 45CPU, and its completely useless. I haven't seen it anywhere else, and when I kill it, I only release my processor from this torment. In fact, I'm going to make a topic itself about it.

But back on topic. I will try those too to see if they can fix something.

I don't recall how XP worked, but I'm thinking that System restore points are chewing up some of your space. Using the Disk Cleanup utility that Echo mentioned, there should be a second tab in that program. Click the tab, then there will be a button to delete all but the most recent restore point. That should free up some space for you.

__________________
"as a fanboy i refuse to admit it and will pull countless things out of my butt to disprove it"

2. This folder I created myself to put files and folders that are broken. I never knew it was this much because when you use properties on them, it says that its 0b. SpaceSniffer found that.
Now, In it , I got these two folders that takes alot of memory